Background: During the 1990-1991 Gulf War, approximately 700,000 service members were deployed to the Gulf region. An additional 4 million were deployed elsewhere or were domestically stationed. Increased symptomatology, including a unique pattern of chronic multi-symptom illness, among this cohort has been well documented. Among the Gulf War I era Veteran population there is evidence of worse functional status, increased experience of symptoms, and, to a lesser-known extent, subsequent potential increases in healthcare utilization. Much of this work was completed in the first ten years after the conflict. At this poit, this Veteran population is approximately age 40-60 years and likely experiencing additional health issues associated with aging, such as cancer and elevated cardiovascular disease risk. Despite the earlier research, significant gaps in knowledge remain regarding the current diagnoses, healthcare utilization patterns, costs, and satisfaction with care of Veterans of this era. Objectives: In order to improve the care Gulf War era Veterans receive, the objectives of this proposal are to establish a comprehensive understanding of Gulf War I era Veterans' documented diagnoses, healthcare utilization patterns and costs, and patient-reported determinants of traditional and non-traditional healthcare utilization, associated healthcare costs, goals of care, and satisfaction. To accomplish these objectives we will pursue three specific aims: (1) describe the demographic and clinical characteristics of VHA users within a stratified random sample of 90,000 Gulf War I era Veterans; (2) describe healthcare utilization patterns and direct care costs incurred by Veterans within our sample, both overall and for pre-specified diagnostic clusters, including chronic multi-system illness, cardiovascular conditions, mental health disorders, cancers, neurodegenerative conditions, and complex chronic disease; and (3) explore Veterans' decision-making perspectives regarding choice of healthcare providers and utilization, and their experiences, goals of care, and satisfaction with the care the have received. In all aims, we will explore differences according to characteristics including Gulf War deployment, sex, age, and other sociodemographic and clinical attributes. Methods: We will use an existing stratified random sample of Gulf War I era Veterans from an existing pool of potential enrollees in the Gulf War Era Cohort and Biorepository (GWECB) project. The GWECB recruitment sample, obtained from the rosters maintained by the Defense Manpower Data Center, is stratified by Gulf War deployment status, service component and branch, grade, race, and sex. For the Veterans in this sample who have ever used VA healthcare (approximately 51,000), we will obtain data about patient characteristics, documented diagnoses, and VA healthcare utilization and costs from the following administrative and clinical data sources: Medical SAS Inpatient and Outpatient files, Decision Support System cost extracts, and HERC average cost datasets. Using these data, we will characterize Veterans' demographic qualities and most common diagnoses and diagnostic clusters (Aim 1) and conduct univariate and multivariate analyses of Veterans' healthcare utilization and associated costs (Aim 2). In Aim 3, we will survey a subsample to assess self-reported utilization of non-traditional forms of care, reliance on VA and non-VA healthcare providers, functional health status, goals of care, and satisfaction with care. Focus groups will be conducted with a subset of survey respondents living in the Durham VA Medical Center catchment area to explore their decision- making perspectives regarding use of VA and non-VA sources of healthcare. The current proposal represents an unprecedented opportunity to identify the unmet needs of Gulf War I era Veterans and to develop new and innovative strategies to improve their healthcare and health outcomes.